Chorionic villus

If the genetic lesion is understood and a specific probe is available, prenatal diagnosis is possible. DNA from cells collected from as little as 10 mL of amniotic fluid (or by chorionic villus biopsy) can be analyzed by Southern blot transfer. A fetus with the restriction pattern AA in Figure 40-10 does not have sickle cell disease, nor is it a carrier. A fetus with the SS pattern will develop the disease. Probes are now available for this type of analysis of many genetic diseases. 

Citrullinemia. Neonates with AS deficiency usually die, and most survivors suffer major brain injury. Patients with a partial deficiency may have a milder course, and a few individuals with citrullinemia have been phenotypi-cally normal. The diagnosis usually is apparent from the hyperammonemia and the extreme hypercitrullinemia. The activity of AS can be determined in both fibroblasts and chorionic villus samples, thus simplifying the problem of antenatal diagnosis. 

The increased risk of trisomy with advanced maternal age motivates more than half of pregnant women in North America to undergo prenatal diagnosis (most commonly, amniocentesis or chorionic villus sampling, discussed in Oiapter 6). Down syndrome can also be screened by assaying maternal serum levels of a-fetoprotein, chorionic gonadotropin, and unconjugated estriol. This so-called triple screen can detect approximately 70% of fetuses with Down syndrome. 

The specimen will be the basis for the analytic analysis. Is it RNA or DNA What is the origin of the tissue Amniocentesis Was it a spontaneous product of conception Were anatomic pathology slides or tissue blocks prepared Are cell lines involved Are these primary or immortalized Was a chorionic villus sampling procedure done Is the sample properly collected peripheral blood The answers to each of these questions should be noted, and considered part of the validation of a useful nucleic acid extraction method. A molecular diagnostics laboratory should adhere to the highest standards in providing services, and prior validation of applicable nucleic acid extraction procedures is a must to ensure high-quality service. 

Prenatal analysis Chorionic villus sampling or cultured amniotic fluid cells... 

Cariolou, M. A., Kakkafitou, A., Manoli, P. Ioannou, P. (1993). Prenatal diagnosis for / -thalassemia by PCR from single chorionic villus. BioTechniques, 15, 32-4. 

Antenatal diagnosis is possible by chorionic villus sampling. 

Sampling of fetal cells. A. Amniotic fluid B. Chorionic villus. 

Jansen MW, Brandenburg H, Wildschut HI, Martens AC, Hagenaars AM, Wladimiroff JW, Veld PA, The effect of chorionic villus sampling on the number of fetal cells isolated from maternal blood and on maternal serum alpha-fetoprotein levels, Prenat. Diagn., 17 953-959, 1997. 

Male fetuses with 50 to 230 copies of the repeat should be asymptomatic, whereas those with more than 230 copies will have fragile X syndrome. Female fetuses with 50 to 230 copies also will be asymptomatic however, it is difficult to predict the extent of mental retardation in female fetuses with more than 230 copies of the repeat. Although hypermethylation of the CpG island is a poor prognostic indicator, it is not always present in DNA extracted from chorionic villus samples (Sutherland et al., 1991). Empiric data showing that female carriers with full mutations have nearly a 50% risk of mental impairment should be considered reliable. 

Blood leukocyte DNA was used for mutation analysis of the carbamoyl phosphate synthetase I (CPSI) gene, and he was found to carry two separate, previously described, disease-causing mutations. Subsequently, the boy suffered global developmental delay, reduced head growth, and a seizure disorder. He had several hospital admissions for episodic hyperammonemia associated with intercurrent viral illnesses. In a subsequent pregnancy, the parents had prenatal diagnosis by molecular analysis of chorionic villus. The fetus was not affected, and a healthy baby was born. 

After incubation for 30 minutes at room temperature, the sample was evaporated to dryness. The residue was dissolved in 100 piL of solvent A and 5 fxL was injected into the Qg reversed-phase column. Formation of product was linear with time with up to 6 mg of protein (human chorionic villus cell homogenate) added. 

Sources of enzyme assayed included human plasma, leukocytes, amniotic fluid, chorionic villus cells, and brain and lung samples obtained at autopsy. 

Wanders RJ, Ruiter JP, Wijburg FA, Zeman J, Klement P, Houstek J. Prenatal diagnosis of systemic disorders of the respiratory chain in cultured chorionic villus fibroblasts by study of ATP-syndiesis in digitonin-permeabiUzed cells. J. Inherit. Metab Dis. 1996 19 133-136. 

Investigate potentially fife-threatening disorders of Hb synthesis in the fetus and is performed at less than 10 weeks gestation on chorionic villus samples... 

Prenatal diagnosis can include fetal ultrasound, maternal serum studies, or sampling of cells from the fetoplacental unit by chorionic villus sampling [CVS at 8 to 10 weeks, amniocentesis at 12 to 18 weeks, or percutaneous umbilical sampling (PUBS) from 16 weeks to term]. 

---